1. Equations of mathematical physics;Tikhonov,1953
2. The theory of electric circuits;Kaller,1956
3. On an extension of problem T for the equation uxx + sign yuyy = 0;Karatoprakliev;Dokl. Akad. Nauk SSSR,1963
4. On the problem of equations of a mixed type;Levrent'ev;Dokl. Akad. Nauk SSSR,1950